A novel genetic strategy reveals unexpected roles of the Swi-Snf-like chromatin-remodeling BAF complex in thymocyte development.
We have developed a general strategy for creating littermates bearing either a tissue-specific point mutation or deletion in any target gene, and used the method to dissect the roles of Brg, the ATPase subunit of the chromatin-remodeling Brg-associated factor (BAF) complex, in early thymocyte development. We found that a point mutation that inactivates the Brg ATPase recapitulates multiple defects previously described for Brg deletion (Chi, T.H., M. Wan, P.P. Lee, K. Akashi, D. Metzger, P. Chambon, C.B. Wilson, and G.R. Crabtree. 2003. Immunity. 19:169-182). However, the point mutant helps reveal unexpected roles of Brg in CD25 repression and CD4 activation. Surprisingly, CD4 activation occurs independently of the Brg ATPase and is perhaps mediated by physical interactions between Brg and the CD4 locus. Our study thus suggests that the BAF complex harbors novel activities that can be necessary and even sufficient for stimulating transcription from an endogenous chromatin template in the absence of Brg-dependent remodeling of that template. We conclude that conditional point mutants, rarely used in mammalian genetics, can help uncover important gene functions undetectable or overlooked in deletion mutants.
Jani
Anant
A
Department of Immunobiology, Yale University Medical School, New Haven, CT 06520, USA.
Wan
Mimi
M
Zhang
Jianmin
J
Cui
Kairong
K
Wu
Jie
J
Preston-Hurlburt
Paula
P
Khatri
Rohini
R
Zhao
Keji
K
Chi
Tian
T
D000818:Animals; D015704:CD4 Antigens / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D017354:Point Mutation; D013601:T-Lymphocytes / Q000502:physiology; D013950:Thymus Gland / Q000166:cytology / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
C494812:Bcl2l1 protein, mouse; D015704:CD4 Antigens; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D009687:Nuclear Proteins; C445179:SWI-SNF-B chromatin-remodeling complex; D014157:Transcription Factors; D051020:bcl-X Protein; C513194:Smarca4 protein, mouse; D004265:DNA Helicases